IT, Information Security and Software Dev

Performing a clean installation with Mac OS X 10.7 “Lion”

Apple has released more information about their upcoming OS Mac OS X 10.7 “Lion” last monday. It is going to be released in July, exclusively through the Mac App Store. This means you can purchase it, and can install it immediately (depending on how fast you can download the 4 GB sized OS). The first question that slipped into my mind was: “How can you perform a clean install?”. Luckily there’s already a solution which developers found out (who could already download a developer preview through the App Store).

If Lion is installed and the hard drive is working correctly

Hold down the OPTION ⌥ key during startup. There should be a hidden partition containing Lion, which you can use to perform a clean install.

Burning Lion to a DVD

After downloading Lion through the App Store, an installation program is added to your system. Right-click (or CTRL + click) on the installer and click on Show Package Contents. Copy the file installESD.DMG to your hard drive, and then use Disk Utility or another utility to burn the contents of the image to a DVD.

Creating a USB Drive

Instead of burning Lion to a DVD, you could also create a USB image. Perform the same steps as above, but then in Disk Utility, use the Restore feature to restore the contents of the installESD.DMG image to a USB drive.